The International Council on Active Aging (ICAA) has released the ICAA Age-Friendly Personal Fitness Trainer Checklist. The worksheet is free at http://www.icaa.cc/consumer/age-friendlyguides.htm. It includes questions to ask a potential personal trainer and instructions on evaluating the answers. The four areas that ICAA recommends covering when interviewing a personal trainer are experience, education, personality, and business practices.
For more information about choosing a personal trainer, read the entire article at http://www.icaa.cc/media/press2011/personal-trainers.htm.